This invention relates to fabrics useful for making sails for sailing vessels and more particularly to a laminated sail fabric having a central layer of scrim arranged in a particular fashion.
The art of sailmaking has evolved toward the use of special materials and sail panel designs that allow the sail to maintain an optimum shape under variable wind conditions and various angles of trim.
In order to provide the desired properties in a woven cloth, high tensile strength yarns may be employed, and it is also known to laminate a film, such as a polyester film, to the cloth. Another possibility is to use a laminate of fine and coarse woven cloths, as described in U.S. Pat. No. 4,554,205. The ability to increase strength and stretch resistance of a sail material is often limited by other practical considerations such as weight, stiffness and tear resistance.
More recently, some woven sailcloths have been made from high strength aramid or "KEVLAR" yarns running in the warp direction and polyester or "DACRON" yarns in the fill direction. Due to the nature of the weaving process and the relative strength of the materials, the warp or machine direction yarns bend or crimp the fill yarns. As a result, the material may stretch and distort in a direction parallel and on a bias to the fill yarns. This weakness may be partly minimized by cutting the sail panels in such a fashion that the warp yarns are aligned with and carry the maximum load generated in the sail.
A recent proposal for a sailcloth may be found in U.S. Pat. No. 4,444,822. This patent discloses a warp knit scrim laminated to a plastic sheet. In use, the material would be cut into panels with the warp yarns aligned with the direction of maximum load, such as disclosed in British patent no. 892,528 or U.S. Pat. No. 3,954,076.
In the use of a film laminated to a cloth or scrim, however, several problems arise Under the current theories, it is not necessary to have stretch resistance on the bias if the panels are installed as previously described. In practice, however, considerable stress is applied along the bias and fill as the sail configuration is changed and also during tacking.
A second problem with the use of film is the resulting stiffness of the material. For example, a laminate having a film of 6 to 8 mils would be desirable to prevent excessive stretch, but the stiffness would be too great to allow proper adjustment to the shape of the sail.
In view of the foregoing, it would be desirable to provide a sail fabric having a relatively thin film layer which is additionally reinforced in the fill or bias direction.